Damper and vehicle seat equipped with the damper

ABSTRACT

A damper  1  includes a vessel  2 ; a partitioning member  6  which partitions an internal space of the vessel  2  into two accommodation chambers  4  and  5  for accommodating a viscous fluid  3  and which is movable with respect to the vessel  2 ; a moving force imparting device  7  for imparting to the partitioning member  6  a moving force in an A 1  direction by the input of rotation in an R 2  direction with respect to the vessel  2 , so that the moving velocity is set to one corresponding to the rotating velocity of that input of rotation; a resilient device  8  for resiliently urging the partitioning member  6  in an A 2  direction; a communicating hole  9  formed in the partitioning member  6 ; and a flow limiting device  10  for limiting the flow of the viscous fluid  3  in the accommodating chamber  4  into the accommodating chamber  5  through the communicating hole  9  when the internal pressure of the viscous fluid  3  accommodated in the accommodating chamber  4  has exceeded a fixed value.

This application claims priority to Japan Application No. 2008-117906filed Apr. 28, 2008, the entire contents of each of which are herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a damper for absorbing an impact, andmore particular to a damper suitable for use in a vehicle seat having aheadrest for supporting the head of a seated person by moving forwardwhen, at the time of such as a collision of a vehicle, the seated personmoves backward due to inertia upon receiving an impact from the rear, aswell as a vehicle seat equipped with the damper.

2. Description of the Related Art

-   Patent Document 1: JP-A-10-181403-   Patent Document 2: JP-A-10-119619-   Patent Document 3: JP-A-11-268566-   Patent Document 4: JP-A-2003-81044-   Patent Document 5: JP-A-2003-176844-   Patent Document 6: JP-A-2005-225334-   Patent Document 7: JP-A-2006-82772-   Patent Document 8: JP-A-2006-88875

In vehicles, vehicle seats have been proposed in which a headrest isadapted to move forward to restrict the head of a seated person at thetime of such as a collision.

Shock absorbing dampers which are used in such vehicle seats arerequired to be such that, in the collision at the time of low speed, theimpact caused by the collision is absorbed softly in order to supportthe head so as not to impart the impact, whereas, in the collision atthe time of high speed, the impact is absorbed with stiffnesscorresponding to the magnitude of the impact at the time of thecollision so as to absorb the impact due to the collision by becomingstiff in order to support the head reliably.

SUMMARY OF THE INVENTION

The present invention has been devised in view of the above-describedaspects, and an object of the invention is to provide a damper capableof softly absorbing an impact when the impact is small, and of becomingstiff and positively holding an impact-absorbed body, e.g., the head,when the impact is large.

Another object of the invention is to provide a vehicle seat equippedwith a transmitting mechanism which is capable of positively moving theheadrest in the forward direction only at the time of such as acollision by properly discriminating the time of such as a collision andthe time of a non-collision, and in which the transmitting mechanism canbe compactly installed in a backrest and the like.

In accordance with one aspect of the invention, there is provided adamper comprising: a vessel; a partitioning member which partitions aninterior of the vessel into two accommodation chambers for accommodatinga viscous fluid in an axial direction of the vessel, and which rotatestogether with the vessel in a direction about an axis of the vessel andis movable with respect to the vessel in the axial direction of thevessel, the partitioning member having at least one communicating holeformed therein so as to allow the two accommodating chambers inside thevessel to communicate with each other; moving force imparting means forimparting to the partitioning member a moving force in one direction inthe axial direction by the input of relative rotation in one directionin the direction about the axis of the vessel with respect to thevessel, so that a moving velocity is set to one corresponding to arotating velocity of that input of rotation; resilient means forresiliently urging the partitioning member in another direction in theaxial direction with respect to the vessel; and flow limiting means forlimiting the flow of the viscous fluid in the accommodating chamber onone direction side in the axial direction into the accommodating chamberon another direction side in the axial direction through thecommunicating hole when the internal pressure of the viscous fluidaccommodated in the accommodating chamber on the one direction side inthe axial direction has exceeded a fixed value owing to the movement ofthe partitioning member in the one direction in the axial direction,wherein the flow limiting means includes a variable passage formingmember having a through hole which, in an end face in the one directionin the axial direction, is open to the accommodating chamber on the onedirection side in the axial direction, and fitted to the partitioningmember movably in the axial direction in such a manner as to oppose atan end face thereof in the other direction of the axial direction an endface in the one direction in the axial direction of the partitioningmember so as to form a cross-section variable passage communicatingwith, at one end thereof, the through hole and, at another end thereof,the communicating hole in cooperation with the end face in the onedirection in the axial direction of the partitioning member; and anannular elastic member surrounding the cross-section variable passageand disposed between the end face in the other direction of the axialdirection of the variable passage forming member and the end face in theone direction in the axial direction of the partitioning member.

According to the damper in accordance with the above-described aspect,in the case of the input of rotation at a low velocity not exceeding afixed value, the partitioning member is moved in one direction in theaxial direction at a low velocity not exceeding the fixed value, and theinternal pressure of the viscous fluid accommodated in the accommodatingchamber on the one direction side in the axial direction of the vesseldoes not exceed a fixed value. Therefore, the annular elastic memberdisposed between the end face in the other direction of the axialdirection of the variable passage forming member and the end face in theone direction in the axial direction of the partitioning member is notgreatly deformed elastically, and a large passage cross section of thecross-section variable passage is maintained. Thus, the viscous fluidaccommodated in the accommodating chamber on the one direction side inthe axial direction is allowed to flow into the accommodating chamber onthe other direction side through the through hole, the cross-sectionvariable passage, and the communicating hole without much resistance. Asa result, a resultant damping force, i.e., a reaction force with respectto the input of rotation, is set to a relatively small value based onthe flow resistance in the case where the viscous fluid flows throughthe through hole, the cross-section variable passage, and thecommunicating hole. On the other hand, in the case of the input ofhigh-speed rotation exceeding the fixed value, the partitioning membertends to be moved in the one direction in the axial direction at a highvelocity exceeding the fixed value, and the internal pressure of theviscous fluid accommodated in the accommodating chamber on the onedirection side in the axial direction of the vessel exceeds a fixedvalue. Therefore, the annular elastic member sandwiched between the endface in the other direction of the axial direction of the variablepassage forming member and the end face in the one direction in theaxial direction of the partitioning member is deformed elastically.Hence, the axial distance between the end face in the other direction ofthe axial direction of the variable passage forming member and the endface in the one direction in the axial direction of the partitioningmember becomes small, so that the passage cross section of thecross-section variable passage becomes small. Thus, large resistanceoccurs in the flow of the viscous fluid accommodated in theaccommodating chamber on the one direction side in the axial directionof the vessel into the accommodating chamber on the other direction sidein the axial direction of the vessel through the through hole, thecross-section variable passage, and the communicating hole. As a result,a resultant damping force, i.e., a reaction force with respect to theinput of rotation, assumes a value which is based on the compressionresistance of the viscous fluid in the accommodating chamber on the onedirection side in the axial direction and the flow resistance of theviscous fluid through the cross-section variable passage having thepassage cross section which has become small. Thus, in the case of theinput of low-speed rotation not exceeding a fixed value in which casethe impact is small, the impact is absorbed softly, whereas in the caseof the input of high-speed rotation exceeding the fixed value in whichcase the impact is large, the damper becomes stiff so as to be able topositively hold the impact-absorbed body.

In a preferred example, the moving force imparting means includes arotatable member disposed in the vessel rotatably in the direction aboutthe axis of the vessel; and inclined surface means having inclinedsurfaces which are formed between an end face in the one direction inthe axial direction of the rotatable member and the end face in theother direction of the axial direction of the partitioning memberopposing that end face in the one direction and which are inclined withrespect to the axial direction. In such a moving force imparting means,the inclined surface means includes a plurality of rotatable memberprojections formed integrally on the end face in the one direction ofthe rotatable member projectingly in the one direction in the axialdirection, and arranged in the direction about the axis, and a pluralityof partitioning member projections formed integrally on the end face inthe other direction of the partitioning member projectingly in the otherdirection of the axial direction, and arranged in the direction aboutthe axis so as to mesh with the rotatable member projections. Further,in the case of the inclined surface means, the inclined surfaces areformed on the rotatable member projections and the partitioning memberprojections, respectively, so as to be brought into sliding contact witheach other.

As for the communicating hole, one communicating hole may be used.Alternatively, however, a plurality of communicating holes may be formedin the partitioning member. In this case, the variable passage formingmember may have a plate-like portion having the through hole, legportions formed integrally on the plate-like portion and respectivelyfitted in the communicating holes, and hook portions which arerespectively formed integrally on end portions of the leg portionsprojecting from the communicating holes so as to prevent the legportions from coming off the communicating holes.

In another preferred example, the partitioning member has a truncatedconical surface in the end face in the one direction in the axialdirection, the variable passage forming member has a truncated conicalsurface which is complementary to the truncated conical surface of thepartitioning member and opposes that truncated conical surface, and thecross-section variable passage has a truncated conical passage formed bythe truncated conical surface of the partitioning member and thetruncated conical surface of the variable passage forming member. In thecase of such an example, the truncated conical surface of thepartitioning member may have one of a truncated conical recessed surfaceand a truncated conical projecting surface, while the truncated conicalsurface of the variable passage forming member may have the other one ofthe truncated conical recessed surface and the truncated conicalprojecting surface.

The annular elastic member in a preferred example is constituted by anO-ring formed of natural rubber or synthetic rubber whose modulus ofelastic is small at a high temperature (the annular elastic memberbecomes soft) and large at a low temperature (the annular elastic memberbecomes hard). The annular elastic member formed such an O-ringundergoes large elastic deformation at high temperature and smallelastic deformation at low temperature. As a result, coupled with thesynergistic action with the viscous fluid having a positive temperaturecharacteristic concerning fluidity whereby the fluidity increases athigh temperature and the fluidity decreases at low temperature, it ispossible to reduce the temperature dependence of the flow resistance ofthe viscous fluid flowing through the cross-section variable passagehaving a passage cross-sectional area determined by the elasticdeformation of the annular elastic member. Thus, it is possible toreduce the difference, for instance, between, on the one hand, thestiffness of the damper in the axial direction in the case of an inputof high-speed rotation exceeding a fixed value in which case the impactbecomes large at high temperature and, on the other hand, the stiffnessof the damper in the axial direction in the case of an input ofhigh-speed rotation exceeding the fixed value in which case the impactbecomes large at low temperature. Hence, it becomes possible topositively hold the impact-absorbed body with stiffness which does notdiffer so much both at high temperature and at low temperature withrespect to the axial direction. In the invention, the annular elasticmember is not limited to one constituted by an O-ring formed of naturalrubber or synthetic rubber, and may be formed of an elastic materialsuch as polyurethane rubber, acrylic rubber, silicone rubber, polyesterelastomer, or the like. Furthermore, the annular elastic member may beconstituted by a ring or the like whose cross-sectional shape is of asquare type, a Y-type, a U-type, a V-type, or an X-type.

As the viscous fluid used in the invention, silicone oil of 100 to 1000cst is suitable, but is not limited to the same.

In accordance with another aspect of the invention, there is provided avehicle seat comprising: a backrest of a vehicle; a headrest supportedby the backrest movably in a forward direction of the vehicle; movementurging means for urging the headrest to move in the forward direction;and an inhibition mechanism for inhibiting the movement of the headrestin the forward direction; and canceling means for canceling theinhibition by the inhibition mechanism of the movement of the headrestin the forward direction when a moving velocity of a force applied tothe backrest in a backward direction of the vehicle has exceeded a fixedvalue, the canceling means having a load-rotation converting mechanismfor converting a load applied to a back receiving portion of thebackrest into a rotational force and a transmitting mechanism fortransmitting to the inhibition mechanism a force applied to the backrestin the backward direction of the vehicle on the basis of the movingvelocity exceeding the fixed value, the transmitting mechanism havingthe damper according to any one of the above-described forms, whereinone of the vessel and the moving force imparting means of the damper iscoupled to the load-rotation converting mechanism so as to receive therotational force from the load-rotation converting mechanism as an inputof rotation, and another one of the vessel and the moving forceimparting means of the damper is coupled to the inhibition mechanism soas to transmit to the inhibition mechanism the force applied to thebackrest in the backward direction of the vehicle on the basis of themoving velocity exceeding the fixed value.

According to the vehicle seat in accordance with the above-describedaspect of the invention, the canceling means, which cancels theinhibition by the inhibition mechanism of the movement of the headrestin the forward direction when a moving velocity of a force applied tothe backrest in a backward direction of the vehicle has exceeded a fixedvalue, has a transmitting mechanism for transmitting to the inhibitionmechanism a force applied to the backrest in the backward direction ofthe vehicle on the basis of the moving velocity exceeding the fixedvalue. Moreover, since the transmitting mechanism has the damperaccording to any one of the above-described forms, it is possible topositively move the headrest in the forward direction only at the timeof such as a collision by properly discriminating the time of such as acollision and the time of a non-collision, and the transmittingmechanism can be compactly installed in the backrest and the like.

In the vehicle seat in accordance with the invention, the load-rotationconverting mechanism may have a load receiving plate supported rotatablyby a frame of the backrest and disposed in the back receiving portion ofthe backrest.

The headrest may be supported by the backrest forwardly rotatably ortranslatably, the movement urging means may be adapted to urge theheadrest to forwardly rotate or translate, and the inhibition mechanismmay be adapted to inhibit the rotation or translation of the headrest inthe forward direction.

According to the invention, it is possible to provide a damper capableof softly absorbing an impact when the impact is small, and of becomingstiff and positively holding an impact-absorbed body, e.g., the head,when the impact is large. In addition, it is possible to provide avehicle seat equipped with a damper which is capable of positivelymoving the headrest in the forward direction only at the time of such asa collision by properly discriminating the time of such as a collisionand the time of a non-collision, and in which the transmitting mechanismcan be compactly installed in the backrest and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory side elevational view of a preferred embodimentof the invention;

FIG. 2 is an explanatory side cross-sectional view of the embodimentshown in FIG. 1;

FIG. 3 is an explanatory exploded view of the embodiment shown in FIG.1;

FIG. 4 is an explanatory partial enlarged view of a vessel in theembodiment shown in FIG. 1;

FIG. 5 is an explanatory partial right side elevational view of thevessel shown in FIG. 4;

FIG. 6 is an explanatory enlarged view of a variable passage formingmember shown in FIG. 2;

FIG. 7 is an explanatory enlarged view of a partitioning member and thelike shown in FIG. 2;

FIG. 8 is an explanatory left side elevational view of the partitioningmember and the like shown in FIG. 7;

FIG. 9 is an explanatory right side elevational view of the partitioningmember and the like shown in FIG. 7;

FIG. 10 is an explanatory enlarged cross-sectional view of thepartitioning member and the like shown in FIG. 2;

FIG. 11 is an explanatory partial enlarged view of a moving forceimparting means and the like shown in FIG. 2;

FIG. 12 is an explanatory left side elevational view of the moving forceimparting means and the like shown in FIG. 11;

FIG. 13 is an explanatory right side elevational view of the movingforce imparting means and the like shown in FIG. 11;

FIG. 14 is an explanatory enlarged cross-sectional view of thepartitioning member, the variable passage forming member, and the likeshown in FIG. 2;

FIG. 15 is a diagram explaining the operation of the embodiment shown inFIG. 1;

FIG. 16 is another diagram explaining the operation of the embodimentshown in FIG. 1;

FIG. 17 is an explanatory side elevational view of an embodiment inwhich the embodiment shown in FIG. 1 is used in a vehicle seat; and

FIG. 18 is an explanatory front elevational view of the embodiment shownin FIG. 17

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereafter, a more detailed description will be given of the mode forcarrying out the invention with reference to the preferred embodimentshown in the drawings. It should be noted that the present invention isnot limited to such an embodiment.

In FIGS. 1 to 5, a damper 1 in accordance with this embodiment iscomprised of a vessel 2; a partitioning member 6 which partitions aninternal space of the vessel 2 into two accommodation chambers 4 and 5for accommodating a viscous fluid 3 in an A1-A2 direction, i.e., in anaxial direction of that vessel 2, and which rotates together with thevessel 2 in an R1-R2 direction, i.e., in a direction about an axis O ofthe vessel 2 and is movable with respect to the vessel 2 in the A1-A2direction, i.e., in the axial direction of the vessel 2; a moving forceimparting means 7 for imparting to the partitioning member 6 a movingforce in an A1 direction, i.e., one direction in the A1-A2 direction, bythe input of relative rotation in an R2 direction, i.e., one directionin the R1-R2 direction, with respect to the vessel 2, so that the movingvelocity is set to one corresponding to the rotating velocity of thatinput of rotation; a resilient means 8 for resiliently urging thepartitioning member 6 in an A2 direction which is the other direction inthe A1-A2 direction; two communicating holes 9 formed in thepartitioning member 6 so as to allow the two accommodating chambers 4and 5 inside the vessel 2 to communicate with each other; and a flowlimiting means 10 for limiting the flow of the viscous fluid 3 in theaccommodating chamber 4 on the A1 direction side into the accommodatingchamber 5 on the A2 direction side through the communicating holes 9when the internal pressure of the viscous fluid 3 accommodated in theaccommodating chamber 4 on the A1 direction side has exceeded a fixedvalue owing to the movement of the partitioning member 6 in the A1direction.

The vessel 2 includes a hollow cylindrical portion 23 integrally havingan inside diameter-side collar portion 21 at its end in the A2 directionand an outside diameter-side collar portion 22 at its end in the A1direction, respectively, as well as a closure member 28 with an armportion 27, the outside diameter-side collar portion 22 of the hollowcylindrical portion 23 being secured to the closure member 28 by rivetsor screws 24, the closure member 28 integrally having on its end 25 inthe A2 direction a plurality of projections projecting in the A2direction, i.e., in this embodiment three semicylindrical projections 26arranged at equiangular intervals in the R1-R2 direction, respectively.

An annular notch 31 for accommodating a seal ring 30 constituted by anO-ring is formed at an end portion in the A1 direction of a cylindricalinner peripheral surface 29 of the inside diameter-side collar portion21. Meanwhile, an annular groove 34 for accommodating a seal ring 33,which is constituted by an O-ring and adapted to be brought intoresilient contact with the end face 25, is formed in an end face 32 inthe A1 direction of the outside diameter-side collar portion 22.

As shown in particular detail in FIGS. 7 to 10, the partitioning member6 includes a disk-shaped body 43 having a cylindrical outer peripheralsurface 42 which is brought into contact movably in the A1-A2 directionwith a cylindrical inner peripheral surface 41 of the hollow cylindricalportion 23; a plurality of, in this embodiment three, semicylindricalprojections 45 projecting integrally in the A1 direction from a radiallyouter edge of an end face 44 in the A1 direction of the disk-shaped body43, and arranged at equiangular intervals in the R1-R2 direction so asto mesh with the three projections 26 without gaps in the R1-R2direction; a large-diameter disk-shaped portion 46 projecting in the A1direction integrally from the end face 44 in the A1 direction of thedisk-shaped body 43; a small-diameter disk-shaped portion 48 projectingin the A1 direction integrally from an end face 47 in the A1 directionof the disk-shaped portion 46; a truncated conical portion 51 projectingin the A1 direction integrally from an end face 49 in the A1 directionof the disk-shaped portion 48 and having a truncated conical surface 50;and a columnar projection 52 projecting in the A1 direction integrallyfrom a projecting end in the A1 direction of the truncated conicalportion 51. Thus, an end face 54 in the A1 direction of the partitioningmember 6 has the end face 44, the end face 47, the end face 49, and thetruncated conical surface 50.

The disk-shaped body 43 has in its outer peripheral surface 42 anannular groove 56 to which a seal ring 55 constituted by an O-ring andadapted to be brought into resilient contact with the inner peripheralsurface 41, and has in its end face 58 in the A2 direction a cylindricalrecess 57 which is open to the accommodating chamber 5. The respectivecommunicating holes 9, which are formed in the disk-shaped body 43, thedisk-shaped portion 46, and the disk-shaped portion 48 of thepartitioning member 6 in such a manner as to oppose each other in theradial direction, are open at their one ends in the A1 direction in theend face 49 of the disk-shaped portion 48, and are open at their otherends in the A2 direction in a depressed end face 59 of the disk-shapedbody 43 defining the bottom surface of the recess 57, to therebycommunicate with the accommodating chamber 5 through the recess 57.

The partitioning member 6 is disposed in the vessel 2 movably in theA1-A2 direction relative to the vessel 2 and immovably in the R1-R2direction relative to the vessel 2, i.e., so as to rotate in the samedirection in conjunction with the rotation of the vessel 2 in the R1-R2direction without rotating in the R1-R2 direction relative to the vessel2. The partitioning member 6 defines the accommodating chamber 4 on theA1 direction side in the internal space of the vessel 2 in cooperationwith the closure member 28.

As shown in particular detail in FIGS. 7, 9, and 10 to 13, the movingforce imparting means 7 includes a rotatable member 61 disposed in theinternal space of the vessel 2 rotatably in the R1-R2 direction relativeto the vessel 2; and an inclined surface means 65 having pluralities of,i.e., in this embodiment respectively three, inclined surfaces 63 and 64which are formed between an end face 62 in the A1 direction of therotatable member 61 and the end face 58 in the A2 direction of thepartitioning member 6 opposing that end face 62 and which are inclinedwith respect to the A1-A2

As shown in particular detail in FIGS. 11 to 13, the rotatable member 61includes a large-diameter disk-shaped body 72 having a cylindrical outerperipheral surface 71 which is brought into contact with the cylindricalinner peripheral surface 41 of the hollow cylindrical portion 23rotatably in the R1-R2 direction, as well as a small-diameter annularportion 75 having a cylindrical outer peripheral surface 74 whichprojects integrally from a central portion of its end face in the A2direction of the disk-shaped body 72 and is brought into contact withthe inner peripheral surface 29 of the inside diameter-side collarportion 21 rotatably in the R1-R2 direction. The rotatable member 61defines the accommodating chamber 5 inside the vessel 2 in cooperationwith the partitioning member 6 and is adapted to not move in the A2direction by coming into contact with the inside diameter-side collarportion 21 at its end face 73 rotatably in the R1-R2 direction, the sealring 30 being in resilient contact with the outer peripheral surface 74of the annular portion 75 and the end face 73 of the disk-shaped body72.

The disk-shaped body 72 and the annular portion 75 have in their centralportions a hexagonal bottomed groove 76. A sectionally hexagonalrotating shaft 77 is adapted to be fitted in the bottomed groove 76, andthe input of relative rotation in the R1-R2 direction with respect tothe vessel 2 is adapted to be applied to the rotatable member 61 by therotating shaft 77.

As shown in particular detail in FIGS. 7 and 9 to 12, the inclinedsurface means 65 includes a plurality of, i.e., in this embodimentthree, rotatable member projections 81 formed integrally on the end face62 of the disk-shaped body 72 of the rotatable member 61 projectingly inthe A1 direction, and arranged at equiangular intervals in the R1-R2direction, as well as a plurality of, i.e., in this embodiment three,partitioning member projections 82 formed integrally on the end face 58of the disk-shaped body 43 of the partitioning member 6 projectingly inthe A2 direction, and arranged at equiangular intervals in the R1-R2direction so as to mesh with the rotatable member projections 81.

Each rotatable member projection 81 has a bottom surface 85perpendicular to the A1-A2 direction and flush with the end face 62 aswell as the inclined surface 63 extending from the bottom surface 85 inan R1 direction (counterclockwise in FIG. 12) with an angle θ1.Meanwhile, each partitioning member projection 82 has an apex surface 86perpendicular to the A1-A2 direction and in contact with the bottomsurface 85 as well as the inclined surface 64 extending from the apexsurface 86 in the R1 direction (clockwise in FIG. 9) with an angle θ2and in contact with the corresponding inclined surface 63. Thus, theinclined surfaces 63 and 64 are respectively formed on the rotatablemember projections 81 and the partitioning member projections 82 so asto be brought into sliding contact with each other in the R1-R2direction.

When the rotatable member 61 is rotated in the same R2 direction by theinput of rotation in the R2 direction from the rotating shaft 77, themoving force imparting means 7 presses the inclined surfaces 64 in theA1 direction while sliding on the inclined surfaces 64 at their inclinedsurfaces 63 rotating in the R2 direction, as shown in FIG. 16, to movethe partitioning member 6 in the A1 direction against the resiliencyfrom the resilient means 8. On the other hand, when the input ofrotation in the R2 direction from the rotating shaft 77 is canceled, theinclined surfaces 64 are pressed against the inclined surfaces 63 in theA2 direction by the resiliency from the resilient means 8 through thepartitioning member 6, thereby allowing the inclined surfaces 63 torotate in the R1 direction while sliding on the inclined surfaces 64. Asa result, the apex surfaces 86 are brought into contact with the bottomsurface 85, so that the partitioning member 6 is returned to itsoriginal moving position, while the rotatable member 61 is returned toits original rotating position. Thus, the moving force in the A1direction is adapted to be imparted to the partitioning member 6 by theinput of relative rotation in the R2 direction with respect to thevessel 2, so that the moving velocity is set to one corresponding to therotating velocity in the R2 direction of the input of the rotation.

The resilient means 8 has a coil spring 88 disposed between the end face25 of the closure member 28 and the end face 44 of the disk-shaped body43 in such a manner as to be compressed with its ends in contact withthese end faces 25 and 44 and to surround the disk-shaped portion 46 andthe disk-shaped portion 48. The disk-shaped body 43 is urged in the A2direction by the resiliency of the coil spring 88 to thereby impart arotating returning force in the R1 direction to the rotatable member 61of the moving force imparting means 7.

As shown in particular detail in FIGS. 6 and 14, the flow limiting means10 includes a variable passage forming member 95 having a through hole92 which, in an end face 91 in the A1 direction, is open to theaccommodating chamber 4 on the A1 direction side, and fitted to thepartitioning member 6 movably in the A1-A2 direction in such a manner asto oppose at an end face 94 in the A2 direction the end face 47, the endface 49, and the truncated conical surface 50 of the end face 54 in theA1 direction of the partitioning member 6 so as to form a cross-sectionvariable passage 93 communicating with, at one end thereof, the throughhole 92 and, at the other end thereof the communicating holes 9 incooperation with the end face 47, the end face 49, and the truncatedconical surface 50 of the end face 54 in the A1 direction of thepartitioning member 6; and an annular elastic member 96 constituted byan O-ring or the like and surrounding the cross-section variable passage93, the annular elastic member 96 being disposed between the end face 94in the A2 direction of the variable passage forming member 95 and theend face 47 of the end face 54 in the A1 direction of the partitioningmember 6.

The variable passage forming member 95 has a circular plate-like portion97 having the through hole 92 with the columnar projection 52 disposedtherein; a pair of leg portions 98 formed integrally on the plate-likeportion 97 in such a manner as to extend in the A2 direction, the pairof leg portions 98 being respectively fitted in the communicating holes9; and hook portions 99 which are respectively formed integrally on endportions of the leg portions 98 projecting from the communicating holes9 and are engaged with the depressed end face 59, as shown in FIG. 15,so as to prevent the leg portions 98 from coming off the communicatingholes 9 in the A1 direction.

The end face 94 has an annular flat surface 100 with which the legportions 98 are integrally formed and which are brought into contactwith the annular elastic member 96 radially outwardly of the legportions 98; and a truncated conical surface 101 which is surrounded bythe flat surface 100, is complementary to the truncated conical surface50 of the partitioning member 6, and opposes that truncated conicalsurface 50.

The cross-section variable passage 93 has a truncated conical passage105 formed by the truncated conical surface 50 of the partitioningmember 6 and the truncated conical surface 101 of the variable passageforming member 95; an inner annular passage 106 communicating with thetruncated conical passage 105 and formed by the end face 49 of thepartitioning member 6 and the flat surface 100; and outer annularpassage 107 communicating with the inner annular passage 106 and formedby the end face 47 of the partitioning member 6 and the flat surface100. The truncated conical passage 105 communicates with theaccommodating chamber 4 through an annular gap between the columnarprojection 52 disposed in the through hole 92 and the plate-like portion97 in that through hole 92, and the inner annular passage 106communicates with the communicating holes 9, while the outer annularpassage 107 at its radially outer edge communicates with theaccommodating chamber 4 when the contact of the flat surface 100 withthe annular elastic member 96 is canceled, as shown in FIG. 15.

The annular elastic member 96 is constituted by an O-ring formed ofnatural rubber or synthetic rubber whose modulus of elastic is small ata high temperature (the annular elastic member becomes soft) and largeat a low temperature (the annular elastic member becomes hard).

In the slow, low-speed movement in the A1 direction of the partitioningmember 6 in which the internal pressure of the viscous fluid 3 in theaccommodating chamber 4 is not very large relative to the internalpressure of the viscous fluid 3 in the accommodating chamber 5, i.e., inthe input of relative low-speed rotation in the R2 direction from therotating shaft 77, the flow limiting means 10 causes the flat surface100 to be brought into pressing contact with the annular elastic member96 being in contact with the end face 47, to such an extent that theannular elastic member 96 is not greatly deformed elastically in itscross section diameter owing to the internal pressure of the viscousfluid 3 in the accommodating chamber 4, as shown in FIG. 16, to therebyblock the outer annular passage 107 and hamper the communication of theaccommodating chamber 4 with the accommodating chamber 5 through theouter annular passage 107. Meanwhile, the accommodating chamber 4 iscommunicated with the accommodating chamber 5 through the truncatedconical passage 105 and the inner annular passage 106 each having apassage cross section determined by the cross section diameter of theannular elastic member 96 which has not been greatly deformedelastically in its cross section diameter, as well as the annular gapbetween the columnar projection 52 and the plate-like portion 97 in thethrough hole 92, the communicating holes 9, and the recess 57. A smallresisting force is thus generated for the slow movement of thepartitioning member 6 in the A1 direction by allowing the flow of theviscous fluid 3 from the accommodating chamber 4 into the accommodatingchamber 5 by the above-described communication.

In the high-speed movement in the A1 direction of the partitioningmember 6 in which the internal pressure of the viscous fluid 3 in theaccommodating chamber 4 becomes extremely large relative to the internalpressure of the viscous fluid 3 in the accommodating chamber 5, i.e., inthe input of relative high-speed rotation in the R2 direction from therotating shaft 77, the flow limiting means 10 causes the plate-likeportion 97 of the variable passage forming member 95 to press againstthe annular elastic member 96 so as to allow the annular elastic member96 to be greatly deformed elastically in its cross section diameter. Thetruncated conical passage 105 and the inner annular passage 106 arethereby narrowed to reduce their passage cross-sectional areas. Theaccommodating chamber 4 is communicated with the accommodating chamber 5through the truncated conical passage 105 and the inner annular passage106 with their passage cross-sectional areas thus reduced. A largeresisting force is thus generated for the high-speed movement of thepartitioning member 6 in the A1 direction by causing the flow of theviscous fluid 3 from the accommodating chamber 4 into the accommodatingchamber 5 with large resistance owing to the above-describedcommunication. Furthermore, in the rotation in the R2 direction of therotatable member 61 due to the input of relative rotation at an evenhigher speed in the R2 direction from the rotating shaft 77, the annularelastic member 96 in its cross section diameter is even more greatlycrushed and deformed elastically by the elastic crushing of the annularelastic member 96 by the plate-like portion 97 of the variable passageforming member 95. Thus, passage cross-sectional areas of the truncatedconical passage 105 and the inner annular passage 106 are set toextremely small values which are determined by the cross sectiondiameter of the annular elastic member 96 which has been crushed anddeformed, thereby reducing the flow of the viscous fluid 3 in theaccommodating chamber 4 into the accommodating chamber 5 to asubstantially extremely small degree and substantially stopping theabove-described high-speed rotation through the partitioning member 6.Hence, the rotation of the impact-absorbed body which tends to rotatethe rotating shaft 77 at high speed is stopped, thereby positivelyholding the impact-absorbed body.

When the input of relative rotation in the R2 direction from therotating shaft 77 ceases after the movement of the partitioning member 6in the A1 direction, as shown in FIG. 16, in the flow limiting means 10,the partitioning member 6 begins to be conversely moved in the A2direction by the resiliency of the coil spring 88. In this movement, thevariable passage forming member 95 is relatively moved in the A1direction with respect to the partitioning member 6, as shown in FIG.15. As a result, the communication between the outer annular passage 107and the accommodating chamber 4 is recovered, and the truncated conicalpassage 105 and the inner annular passage 106 each having a largepassage cross section are formed, thereby causing the flow of theviscous fluid 3 from the accommodating chamber 4 into the accommodatingchamber 5 with small resistance. Hence, the partitioning member 6 isspeedily moved in the A2 direction with such a small resisting force,and the rotatable member 61 is returned to its initial position in whichthe respective apex surfaces 86 are in contact with the respectivecorresponding bottom surfaces 85.

The annular elastic member 96 made of natural rubber or synthetic rubberhaving a small modulus of elasticity at high temperature and a largemodulus of elasticity at low temperature undergoes large elasticdeformation at high temperature and small elastic deformation at lowtemperature. Therefore, coupled with the synergistic action with theviscous fluid 3 having a positive temperature characteristic concerningfluidity whereby the fluidity increases at high temperature and thefluidity decreases at low temperature, it is possible to reduce thetemperature dependence of the flow resistance of the viscous fluidflowing through the cross-section variable passage 93 having a passagecross-sectional area determined by the elastic deformation of theannular elastic member 96. Thus, it is possible to reduce thedifference, for instance, between, on the one hand, the stiffness of thedamper 1 in the A2 direction in the case of an input of high-speedrotation exceeding a fixed value in which case the impact becomes largeat high temperature and, on the other hand, the stiffness of the damper1 in the A2 direction in the case of an input of high-speed rotationexceeding the fixed value in which case the impact becomes large at lowtemperature. Hence, it becomes possible to positively hold theimpact-absorbed body with stiffness which does not differ so much bothat high temperature and at low temperature with respect to the A2direction.

The above-described damper 1 may be used for a vehicle seat 201, asshown in FIGS. 17 and 18. Namely, the vehicle seat 201 in accordancewith this embodiment is comprised of a seat 203 mounted on a floor 202of a vehicle such that its front-back position and inclined position areadjustable; a vehicle backrest 204 installed to the seat 203 such thatits inclined position is adjustable; a headrest 205 supported by thebackrest 204 movably in the forward direction, i.e., rotatably in aforward R3 direction in this embodiment; a rotatively urging means 206for rotatively urging the headrest in the forward R3 direction; and aninhibition mechanism 207 for inhibiting the rotation of the headrest 205in the R3 direction; and a canceling means 208 for canceling theinhibition by the inhibition mechanism 207 of the movement of theheadrest 205 in the R3 direction when the moving velocity of the forceapplied to the backrest 204 in the backward direction of the vehicle hasexceeded a fixed value.

Since the mechanism of mounting the seat 203 on the floor 202 such thatits front-back position and inclined position are adjustable and themechanism of installing the backrest 204 to the seat 203 such that itsinclined position is adjustable are publicly known, a detaileddescription thereof will be omitted.

The headrest 205 has a headrest body 211 and a supporting member 213which is secured to the headrest body 211 and is supported by a frame(not shown) of the backrest 204 rotatably in the R3 direction by meansof a shaft 212. The supporting member 213 is adapted to not rotate in anopposite direction to the R3 direction by a stopper 214 secured to theframe of the backrest 204.

The rotatively urging means 206 serving as a movement urging means has acoil spring 215 having one end secured to the frame of the backrest 204and the other end secured to the supporting member 213, so as toconstantly urge the headrest 205 rotatively in the R3 direction by theresiliency of the coil spring 215.

The inhibition mechanism 207 has a hook member 217 which is supported bya frame of the backrest 204 by means of a shaft 216 rotatably in an R4direction and abuts against and engages a leading end of the supportingmember 213 so as to inhibit the rotation of the supporting member 213 inthe R3 direction, as well as a stopper 218 and a coil spring 219 forsetting the hook member 217 to an abutting and engaging position withrespect to the leading end of the supporting member 213.

The canceling means 208 has a load-rotation converting mechanism 222which is displaced by the load applied to a back receiving portion 221of the backrest 204 from an occupant seated in the seat 203 and atransmitting mechanism 223 which transmits to the inhibition mechanism207 a force applied to the back receiving portion 221 of the backrest204 in the backward direction of the vehicle on the basis of itsvelocity exceeding a fixed value, but which does not transmit to theinhibition mechanism 207 the force applied to the back receiving portion221 of the backrest 204 on the basis of its velocity of the fixed valueor less.

The load-rotation converting mechanism 222 has the rotating shaft 77supported rotatably by the frame of the backrest 204 and a loadreceiving plate 225 secured to the rotating shaft 77 and disposed in theback receiving portion 221 of the backrest 204. The load receiving plate225 supported rotatably by the frame of the backrest 204 by means of therotating shaft 77 is embedded in a cushion in the back receiving portion221 of the backrest 204.

The transmitting mechanism 223 has a supporting shaft 226 supported bythe frame of the backrest 204, the damper 1 supported at the closuremember 28 of the vessel 2 by the supporting shaft 226 rotatably in theR1-R2 direction, and a wire 227 having one end coupled to the arm member27 of the damper 1 and the other end coupled to the hook member 217.

In the damper 1 in accordance with this embodiment, a recess forreceiving one end of the supporting shaft 226 is formed in the other endface 229 of the closure member 28, and the vessel 2 of the damper 1 issupported by the frame of the backrest 204 rotatably about thesupporting shaft 226 in the R1-R2 direction. The rotating shaft 77having a hexagonal cross section is fitted in the hexagonal bottomedgroove 76 in the central portions of the disk-shaped body 72 and theannular portion 75. Thus, the vessel 2 of the damper 1 is semi-fixed bythe resiliency of the coil spring 219 by means of the wire 227 and thehook member 217 in the R2 direction.

In the above-described vehicle seat 201, in a case where the occupant isseated in the seat 203 and the occupant's normal load is applied to thebackrest 204 in the backward direction of the vehicle, or in a casewhere the occupant's load is added to the backrest 204 in the backwarddirection of the vehicle due to the normal acceleration of the vehiclefor the occupant seated in the seat 203, these loads upon the backrest204 are applied slowly at a velocity of a fixed value or less. As aresult, the load receiving plate 225 which receives such a load of theoccupant is rotated slowly about the rotating shaft 77 in the R2direction without causing the vessel 2 semi-fixed with respect to therotation in the R2 direction by the resiliency of the coil spring 219 toproduce rotation in the R2 direction. This slow rotation of the loadreceiving plate 225 produces slow flow of the viscous fluid 3 from theaccommodating chamber 4 into the accommodating chamber 5 through thetruncated conical passage 105 and the inner annular passage 106 eachhaving a passage cross section determined by the cross section diameterof the annular elastic member 96 which has not been greatly deformedelastically, as well as the annular gap between the columnar projection52 and the plate-like portion 97 in the through hole 92, thecommunicating holes 9, and the recess 57. In consequence, the loadreceiving plate 225 and, hence, the backrest 204 are subjected to amoderate impact. Meanwhile, in such slow rotation of the load receivingplate 225, the rotatable member 61 is idled in the R2 direction withrespect to the partitioning member 6 by the inclined surface means 65,so that the rotatable member 61 and the vessel 2 are set in anon-coupled state with respect to the rotation in the R2 direction. As aresult, a tensile force which produces the rotation in the R4 directionof the hook member 217 such as to cancel the abutment and engagementwith the leading end of the supporting member 213 is not produced in thewire 227 through the vessel 2. Thus, the inhibition mechanism 207inhibits the rotation of the headrest 205 in the forward R3 direction,thereby maintaining the headrest 205 in its normal position.

On the other hand with the vehicle seat 201, when, upon a collision fromthe rear, a large velocity in the backward direction exceeding a fixedvalue has occurred in the occupant seated in the seat 203, and the loadreceiving plate 225 is suddenly rotated about the rotating shaft 77 inthe R1 direction, this rotation of the rotating shaft 77 in the R2direction at the velocity exceeding the fixed value limits the flow ofthe viscous fluid 3 from the accommodating chamber 4 into theaccommodating chamber 5 by the truncated conical passage 105 and theinner annular passage 106 each having a passage cross section determinedby the cross section diameter of the annular elastic member 96 which hasbeen greatly deformed elastically. As a result, the rotatable member 61and the vessel 2 are set in a coupled state with respect to the rotationin the R2 direction through the partitioning member 6. In consequence,such rotation of the rotating shaft 77 in the R2 direction at a velocityexceeding the fixed value causes the vessel 2 to undergo rotation aboutthe supporting shaft 226 in the R2 direction through the rotatablemember 61 and the partitioning member 6 by overcoming the resiliency ofthe coil spring 219. Thus, a tensile force producing the rotation of thehook member 217 so as to cancel the abutment and engagement with theleading end of the supporting member 213 is produced in the wire 227.Hence, the hook member 217 of the inhibition mechanism 207 is rotatedabout the shaft 216 in the R4 direction so as to cancel the abutment andengagement with the leading end of the supporting member 213, with theresult that the headrest 205 is rotated in the R3 direction by beingurged by the coil spring 215 so as to hold the occupant's head.

Thus, the vehicle seat 201 has the transmitting mechanism 223 equippedwith the damper 1 serving as a switching mechanism whereby the forceapplied to the backrest 204 in the backward direction of the vehicle ata velocity exceeding a fixed value is transmitted to the inhibitionmechanism 207 so as to cancel the inhibition by the inhibition mechanism107 of the rotation of the headrest 205 in the forward R3 direction,whereas the force applied to the backrest 204 at a velocity of the fixedvalue or less is not transmitted to the inhibition mechanism 207 so asto maintain the inhibition by the inhibition mechanism 107 of therotation of the headrest 205 in the forward R3 direction. Therefore, itis possible to positively move the headrest 205 in the forward R3direction only at the time of such as a collision by properlydiscriminating the time of such as a collision and the time of anon-collision.

In the example of the above-described seat 201, the resetting of theabutment and engagement of the leading end of the supporting member 213with respect to the hook member 217 can be effected if, after themovement of the headrest 205 in the forward R3 direction, the headrest205 is forcibly rotated in the opposite direction to the direction toallow the leading end of the supporting member 213 to slide on aninclined surface of the hook member 217 and to reversely rotate the hookmember 217. It should be noted that although the wire 227 is used in theabove-described embodiment it is possible to alternatively use a gearmechanism, a rack and pinion mechanism, or the like.

1. A damper comprising: a vessel; a partitioning member which partitionsan interior of said vessel into two accommodation chambers foraccommodating a viscous fluid in an axial direction of said vessel, andwhich rotates together with said vessel in a direction about an axis ofsaid vessel and is movable with respect to said vessel in the axialdirection of said vessel, said partitioning member having at least onecommunicating hole formed therein so as to allow the two accommodatingchambers inside said vessel to communicate with each other; moving forceimparting means for imparting to said partitioning member a moving forcein one direction in the axial direction by the input of relativerotation in one direction in the direction about the axis of said vesselwith respect to said vessel, so that a moving velocity is set to onecorresponding to a rotating velocity of that input of rotation;resilient means for resiliently urging said partitioning member inanother direction in the axial direction with respect to said vessel;and flow limiting means for limiting the flow of the viscous fluid inthe accommodating chamber on one direction side in the axial directioninto the accommodating chamber on another direction side in the axialdirection through the communicating hole when the internal pressure ofthe viscous fluid accommodated in the accommodating chamber on the onedirection side in the axial direction has exceeded a fixed value owingto the movement of said partitioning member in the one direction in theaxial direction, wherein said flow limiting means includes a variablepassage forming member having a through hole which, in an end face inthe one direction in the axial direction, is open to the accommodatingchamber on the one direction side in the axial direction, and fitted tosaid partitioning member movably in the axial direction in such a manneras to oppose at an end face thereof in the another direction of theaxial direction an end face in the one direction in the axial directionof said partitioning member so as to form a cross-section variablepassage communicating with, at one end thereof, the through hole and, atanother end thereof, the communicating hole in cooperation with the endface in the one direction in the axial direction of said partitioningmember; and an annular elastic member surrounding the cross-sectionvariable passage and disposed between the end face in the anotherdirection of the axial direction of said variable passage forming memberand the end face in the one direction in the axial direction of saidpartitioning member, wherein a plurality of communication holes areformed in said partitioning member, and said variable passage formingmember has a plate-like portion having the through hole, leg portionsformed integrally on the plate-like portion and respectively fitted inthe communicating holes, and hook portions which are respectively formedintegrally on end portions of the leg portions projecting from thecommunicating holes so as to prevent the leg portions from coming offthe communicating holes.
 2. The damper according to claim 1, whereinsaid moving force imparting means includes a rotatable member disposedin said vessel rotatably in the direction about the axis of said vessel;and inclined surface means having inclined surfaces which are formedbetween an end face in the one direction in the axial direction of saidrotatable member and the end face in the another direction of the axialdirection of said partitioning member opposing that end face in the onedirection and which are inclined with respect to the axial direction. 3.The damper according to claim 2, wherein said inclined surface meansincludes a plurality of rotatable member projections formed integrallyon the end face in the one direction of said rotatable memberprojectingly in the one direction in the axial direction, and arrangedin the direction about the axis, and a plurality of partitioning memberprojections formed integrally on the end face in the other direction ofsaid partitioning member projectingly in the another direction of theaxial direction, and arranged in the direction about the axis so as tomesh with the rotatable member projections, and wherein the inclinedsurfaces are formed on the rotatable member projections and thepartitioning member projections, respectively, so as to be brought intosliding contact with each other.
 4. The damper according to claim 1,wherein said partitioning member has a truncated conical surface in theend face in the one direction in the axial direction, said variablepassage forming member has a truncated conical surface which iscomplementary to the truncated conical surface of said partitioningmember and opposes that truncated conical surface, and the cross-sectionvariable passage has a truncated conical passage formed by the truncatedconical surface of said partitioning member and the truncated conicalsurface of said variable passage forming member.
 5. The damper accordingto claim 1, wherein said annular elastic member is constituted by anO-ring formed of natural rubber or synthetic rubber whose modulus ofelastic is small at a high temperature and large at a low temperature.6. A vehicle seat comprising: a backrest of a vehicle; a headrestsupported by said backrest movably in a forward direction of thevehicle; movement urging means for urging said headrest to move in theforward direction; and an inhibition mechanism for inhibiting themovement of said headrest in the forward direction; and canceling meansfor canceling the inhibition by said inhibition mechanism of themovement of said headrest in the forward direction when a movingvelocity of a force applied to said backrest in a backward direction ofthe vehicle has exceeded a fixed value, said canceling means having aload-rotation converting mechanism for converting a load applied to aback receiving portion of said backrest into a rotational force and atransmitting mechanism for transmitting to said inhibition mechanism aforce applied to said backrest in the backward direction of the vehicleon the basis of the moving velocity exceeding the fixed value, saidtransmitting mechanism having said damper according to claim 1, whereinone of said vessel and said moving force imparting means of said damperis coupled to said load-rotation converting mechanism so as to receivethe rotational force from said load-rotation converting mechanism as aninput of rotation, and another one of said vessel and said moving forceimparting means of said damper is coupled to said inhibition mechanismso as to transmit to said inhibition mechanism the force applied to saidbackrest in the backward direction of the vehicle on the basis of themoving velocity exceeding the fixed value.
 7. The vehicle seat accordingto claim 6, wherein said load-rotation converting mechanism has a loadreceiving plate supported rotatably by a frame of said backrest anddisposed in the back receiving portion of said backrest.
 8. The vehicleseat according to claim 6, wherein said headrest is supported by saidbackrest forwardly rotatably, said movement urging means is adapted tourge said headrest to forwardly rotate, and said inhibition mechanism isadapted to inhibit the rotation of said headrest in the forwarddirection.
 9. A damper comprising: a vessel; a partitioning member whichpartitions an interior of said vessel into two accommodation chambersfor accommodating a viscous fluid in an axial direction of said vessel,and which rotates together with said vessel in a direction about an axisof said vessel and is movable with respect to said vessel in the axialdirection of said vessel, said partitioning member having at least onecommunicating hole formed therein so as to allow the two accommodatingchambers inside said vessel to communicate with each other; moving forceimparting means for imparting to said partitioning member a moving forcein one direction in the axial direction by the input of relativerotation in one direction in the direction about the axis of said vesselwith respect to said vessel, so that a moving velocity is set to onecorresponding to a rotating velocity of that input of rotation;resilient means for resiliently urging said partitioning member inanother direction in the axial direction with respect to said vessel;and flow limiting means for limiting the flow of the viscous fluid inthe accommodating chamber on one direction side in the axial directioninto the accommodating chamber on another direction side in the axialdirection through the communicating hole when the internal pressure ofthe viscous fluid accommodated in the accommodating chamber on the onedirection side in the axial direction has exceeded a fixed value owingto the movement of said partitioning member in the one direction in theaxial direction, wherein said flow limiting means includes a variablepassage forming member having a through hole which, in an end face inthe one direction in the axial direction, is open to the accommodatingchamber on the one direction side in the axial direction, and fitted tosaid partitioning member movably in the axial direction in such a manneras to oppose at an end face thereof in the another direction of theaxial direction an end face in the one direction in the axial directionof said partitioning member so as to form a cross-section variablepassage communicating with, at one end thereof, the through hole and, atanother end thereof, the communicating hole in cooperation with the endface in the one direction in the axial direction of said partitioningmember; and an annular elastic member surrounding the cross-sectionvariable passage and disposed between the end face in the anotherdirection of the axial direction of said variable passage forming memberand the end face in the one direction in the axial direction of saidpartitioning member, wherein said annular elastic member is constitutedby an O-ring formed of natural rubber or synthetic rubber whose modulusof elastic is small at a high temperature and large at a lowtemperature.
 10. The damper according to claim 9, wherein said movingforce imparting means includes a rotatable member disposed in saidvessel rotatably in the direction about the axis of said vessel; andinclined surface means having inclined surfaces which are formed betweenan end face in the one direction in the axial direction of saidrotatable member and the end face in the another direction of the axialdirection of said partitioning member opposing that end face in the onedirection and which are inclined with respect to the axial direction.11. The damper according to claim 10, wherein said inclined surfacemeans includes a plurality of rotatable member projections formedintegrally on the end face in the one direction of said rotatable memberprojectingly in the one direction in the axial direction, and arrangedin the direction about the axis, and a plurality of partitioning memberprojections formed integrally on the end face in the other direction ofsaid partitioning member projectingly in the another direction of theaxial direction, and arranged in the direction about the axis so as tomesh with the rotatable member projections, and wherein the inclinedsurfaces are formed on the rotatable member projections and thepartitioning member projections, respectively, so as to be brought intosliding contact with each other.
 12. The damper according to claim 9,wherein a plurality of communication holes are formed in saidpartitioning member, and said variable passage forming member has aplate-like portion having the through hole, leg portions formedintegrally on the plate-like portion and respectively fitted in thecommunicating holes, and hook portions which are respectively formedintegrally on end portions of the leg portions projecting from thecommunicating holes so as to prevent the leg portions from corning offthe communicating holes.
 13. The damper according to claim 9, whereinsaid partitioning member has a truncated conical surface in the end facein the one direction in the axial direction, said variable passageforming member has a truncated conical surface which is complementary tothe truncated conical surface of said partitioning member and opposesthat truncated conical surface, and the cross-section variable passagehas a truncated conical passage formed by the truncated conical surfaceof said partitioning member and the truncated conical surface of saidvariable passage forming member.
 14. A vehicle seat comprising: abackrest of a vehicle; a headrest supported by said backrest movably ina forward direction of the vehicle; movement urging means for urgingsaid headrest to move in the forward direction; and an inhibitionmechanism for inhibiting the rotation of said headrest in the forwarddirection; and canceling means for canceling the inhibition by saidinhibition mechanism of the movement of said headrest in the forwarddirection when a moving velocity of a force applied to said backrest ina backward direction of the vehicle has exceeded a fixed value, saidcanceling means having a load-rotation converting mechanism forconverting a load applied to a back receiving portion of said backrestinto a rotational force and a transmitting mechanism for transmitting tosaid inhibition mechanism a force applied to said backrest in thebackward direction of the vehicle on the basis of the moving velocityexceeding the fixed value, said transmitting mechanism having saiddamper according to claim 10, wherein one of said vessel and said movingforce imparting means of said damper is coupled to said load-rotationconverting mechanism so as to receive the rotational force from saidload-rotation converting mechanism as an input of rotation, and anotherone of said vessel and said moving force imparting means of said damperis coupled to said inhibition mechanism so as to transmit to saidinhibition mechanism the force applied to said backrest in the backwarddirection of the vehicle on the basis of the moving velocity exceedingthe fixed value.
 15. The vehicle seat according to claim 14, whereinsaid load-rotation converting mechanism has a load receiving platesupported rotatably by a frame of said backrest and disposed in the backreceiving portion of said backrest.
 16. The vehicle seat according toclaim 14, wherein said headrest is supported by said backrest forwardlyrotatably, said movement urging means is adapted to urge said headrestto forwardly rotate, and said inhibition mechanism is adapted to inhibitthe rotation of said headrest in the forward direction.